The present invention relates to improvements in torque transmitting apparatus, and more particularly to improvements in hydrokinetic torque converters of the type often utilized in the power trains of motor vehicles, e.g., to transit torque between the output element of a prime mover (such as a crankshaft or a camshaft of a combustion engine) and the input shaft of a change-speed transmission.
A torque converter of the character to which the present invention pertains normally comprises a rotary housing which is driven by the prime mover and drives a vaned pump, a vaned turbine which can be rotated by the body of fluid filling the housing and being circulated by the pump when the prime mover is on, an optional stator between the pump and the turbine, and a so-called bypass clutch or lockup clutch (hereinafter called bypass clutch) which can be engaged to transmit torque from the housing directly to the turbine or to a hub which rotates with the turbine and serves to transmit torque to the input shaft of the transmission.
The bypass clutch can operate with or without slip and is engageable and disengageable by moving a piston into or from full or partial frictional engagement with a portion of the housing or with a part which rotates with the housing. The housing contains two fluid-filled plenum chambers and the piston is moved axially to partly or fully engage or disengage the clutch in response to changes of pressure differential between the bodies of fluid filling the two plenum chambers. The torque converter often further comprises one or more torsional vibration dampers operating between the housing and the turbine and/or between the turbine and the hub.
A torque converter of the above outlined character is disclosed, for example, in German patent No. 36 14 158. The patented apparatus employs a bypass clutch which operates between the housing and an axially movable piston which rotates with the hub. Such apparatus are known as twin-channel torque converters wherein the piston of or for the bypass clutch separates the plenum chambers from each other when the bypass clutch is at least partially engaged so that a friction lining on the piston engages and receives torque from a portion (e.g., a radial wall) of the housing or from a friction lining on the housing. Partial engagement of the bypass clutch involves a slip of the piston relative to the housing and/or vice versa, and such slip results in the generation of heat in such quantities that the fluid medium in the housing of the torque converter is not always capable of absorbing excess heat. Excessive heating of friction linings forming part of the bypass clutch can entail damage to and frequently rapid destruction of the friction linings; in addition, overheating can adversely influence the hydraulic fluid in the housing of the torque converter.
Abrupt full engagement of the bypass clutch, i.e., without slip, is likely to be even more damaging to the torque converter and can also adversely affect the comfort to the occupant(s) of the motor vehicle. Thus, an abrupt transition from disengagement to full engagement of the bypass clutch can be a cause of discomfort to the occupant(s). In other words, the ride is much more comfortable if the bypass clutch of the torque converter is engaged gradually with an initially pronounced and thereupon gradually decreasing slip, i.e., with the generation of large quantities of undesirable friction heat. Thus, it is desirable to devise a torque converter wherein the bypass clutch is fully engaged upon a gradual reduction of slip but the thus developing large quantities of friction heat can be dissipated and/or otherwise disposed of without affecting the comfort to the occupant(s) of the motor vehicle (if the torque converter is installed in the power train of a motor vehicle) and without damage to the friction linings and/or other heat-sensitive parts of the torque converter and of its bypass clutch. Such requirements cannot be met, or cannot be adequately satisfied, by presently known torque converters. It is also desirable and important to ensure that the withdrawal of requisite quantities of heat be effected without unduly increasing the space requirements of the torque converter, especially in the power train of a motor vehicle.